1. Field of the Invention
The present invention relates to a liquid discharge recording apparatus that records on a recording material by discharging recording liquid. The invention also relates to a liquid supplying device used therefore.
2. Related Background Art
As a mode of a recording apparatus that forms images (characters, graphics, patterns, and the like are called images inclusively) on a recording material, such as recording sheet, there is an ink jet recording apparatus that discharges micro ink droplets from fine discharge ports. Generally, the ink jet recording apparatus provided with a recording head having nozzles used for discharge ink droplets, and an ink that contains ink to be supplied to the recording head. Then, ink is induced from the ink tank to the recording head, and the energy-generating element, such as heat generating element or piezoelectric element, which is installed near the discharge port of each nozzle of the recording head, is driven in accordance with recording signals to discharge ink droplets from each discharge port for recording by the adhesion thereof to a recording material. This ink jet recording apparatus is the so-called non-impact type recording apparatus that makes it possible to perform high-speed recording, and record on various kinds of recording mediums, and has an advantage, among others, that almost no noise is generated at the time of recording, thus being popularized and widely used.
For an ink jet recording apparatus of the kind, it is required to keep ink always under a negatively pressurized condition at the discharge port in order port, with the exception of a designated amount of micro ink droplets to be discharged, that is, to prevent ink leakage from the discharge port when driving is not given (recording on standby or the like), and also, to prevent any excessive ink flow out from the discharge port in the process of recording.
Conventionally, in order to keep ink under a negatively pressurized condition, a structure is adopted to make the height of the ink tank that contains ink lower than that of the discharge port for the utilization of water-level difference. Then, in order to keep the holding pressure of ink regulated by such water-head difference at a constant level under any circumstances, there is a need for the ink tank to be capable of changing the volume thereof in accordance with the amount of ink retained therein. For example, the structure should be arranged so that when the amount of ink inside the ink tank is reduced by a supply of ink to a recording head, the volume of the ink tank is reduced accordingly or when the amount of ink inside the ink tank is increased with a flow-in of ink from the recording head, the volume of the ink tank is increased accordingly. In generally, therefore, a flexible container, such as an aluminum-laminated bag, is used.
FIG. 8 is a view that schematically shows the structure of an ink jet recording apparatus provided with the conventional ink-supplying device. This apparatus has a recording head 110 of ink jet method that records by discharging ink, and an ink supplying device that supplies ink to the recording head 110.
The ink supplying device is provided with an aluminum-laminated flexible bag (ink tank) 210; a tank case 200, which is a highly robust housing to cover the aluminum-laminated bag 210; an ink supply tube 170, which is a pipe type connecting member to supply ink from the aluminum-laminated bag 210 to the recording head 110; and a joint 190 that couples the ink supply tube 170 with the aluminum-laminated bag 210.
The recording head 110 is provided with nozzles 150 that discharge ink; a common liquid chamber 140 serving as a pool to supply ink evenly to each of the nozzles 150; a sub-tank 120 that provisionally retains ink supplied from the ink supplying device before being supplied to the common liquid chamber 140; a filter 130 for removing dust particles contained in ink supplied from the sub-tank 120 to the common liquid chamber 140; and ink suction tube 180 for sucking ink by use of a pump (not shown) when ink is supplied for the first time to a recording head yet to be used.
For this ink jet recording apparatus, the aluminum-laminated bag 210 is filled with ink to form a closed space where no air is present. Ink is supplied to the recording head 110 from the aluminum-laminated bag 210 through the joint 190 and the ink supply tube 170. Inside the recording head 110, a certain amount of ink is retained in the sub-tank 120. Then, from the sub-tank 120, ink is supply to each of the nozzles 150 through the common liquid chamber 140. The sub-tank 120 is not filled with ink up to its total capacity, but there is a remaining portion to enable the air to be accumulated. Also, a rubber plug, valve, or the like (not shown) is used here to airtightly close the ink suction tube 180 so as not to allow ink leakage. At the tip of each nozzle 150, meniscus of ink 160 is formed, and by the surface tension of the meniscus 160, ink is held near the discharge port at the tip of nozzle 150 so as not to allow it to drop down. At this juncture, the aluminum-laminated bag 210 is positioned lower than the recording head 110 to generate a water-head difference h between the discharge port at the tip of nozzle 150 and the ink outlet of the aluminum-laminated bag 210 (the portion where the joint 190 is installed) so that the meniscus of ink 160 is positioned appropriately inside the nozzle 150, while making it possible to prevent ink from being dropped down by enabling the surface tension work appropriately.
In this conventional ink jet recording apparatus, when the inner temperature of the recording head 110 rises due to heat generation or the like along with the recording operation, the air in the sub-tank 120 expands to increase the inner pressure of the sub-tank 120. Then, ink in the sub-tank 120 flows inversely to the ink tank 200 through the ink supply tube 170, thus eliminating the pressure increase in the sub-tank 120. The ink thus inversely flows is contained in the aluminum-laminated bag 210. The aluminum-laminated flexible bag is deformed to swell. In this way, it deals with the increased amount of ink along with the inverse flow of ink form the recording head 110. As a result, the negatively pressurized condition of ink in the recording head 110 is kept at a constant level, and no change occurs in the meniscus 160 that prevents ink from being dropped down.
Also, in the ink jet recording apparatus, when ink inside the recording head 110 is consumed by the recording operation, ink inside the sub-tank 120 is reduced to lower the pressure in the sub-tank 120. Therefore, the ink inside the aluminum-laminated bag 210 flows in the sub-tank 120 through the ink supply tube 170 to eliminate lowering the pressure in the sub-tank 120. In this way, ink in the aluminum-laminated bag 210 is reduced to deform the aluminum-laminated flexible bag 210 for the performance of smooth ink supply.
In this manner, by the flow of ink between the sub-tank 120 and the aluminum-laminated bag 210, it is possible to keep the negatively pressured condition of ink in the recording head 110 at a constant level. In other words, the increase or decrease of pressure in the recording head 110 and in the entire system of the ink supplying device is absorbed by the increase or decrease of the capacity resulting from the deformation of the aluminum-laminated bag 210.
As described above, for the conventional ink jet recording apparatus, pressure exerted on ink is adjusted by the deformation of the aluminum-laminated flexible bag 210 in order to prevent ink from dropping down, while making the smooth ink supply possible. Therefore, it is required for the aluminum-laminated bag 210 to be flexible and deformable. Further, in order not to impede the deformation of the aluminum-laminated bag 210, particularly, not to impede increasing volume thereof, it is required to provide a sufficient space around the aluminum-laminated bag 210. For example, in the structure shown in FIG. 8, the tank case 200 that surrounds the aluminum-laminated bag 210 should be formed to provide a large volume so as not to impede a large swelling of the aluminum-laminated bag 210. This is the cause that the entire size of an ink jet recording apparatus should be made larger inevitably.
Meanwhile, in recent years, an ink jet recording apparatus is used even in a case where a large amount of prints is needed along with the higher speed capability, higher durability, quietness, lower running costs, and other enhanced performance, which are made available for an ink jet recording apparatus. It is also required to make the capacity of an ink tank larger to retain more ink accordingly. The ink jet recording method also makes it easier to provide images in colors, and in recent years, most of ink jet recording apparatus can record in colors. As a result, not only one black color, but also, ink of many colors, such as four colors, six colors, or seven colors, are needed, thus requiring many numbers of large-volume ink tanks to serve the purpose. This naturally causes an ink jet recording apparatus to be made larger eventually. Under such circumstances, the conventional structure as shown in FIG. 8 that uses the aluminum-laminated flexible bag 210 or some other deformable ink tank, and requires the security of space outside the ink tank, becomes extremely unfavorable in terms of the voluminal efficiency in retaining ink. As compared with the capacity of retainable ink, the volume that such pace occupies in the ink supply device is large.
As described above, there are many causes overlapping that make the conventional ink jet recording apparatus larger inevitably, and the status quo is such that it is extremely difficult to meet the requirement of downsizing and lighter weight of the apparatus for which the serviceability or the like is taken into consideration. Ultimately, for the conventional ink jet recording apparatus, it is utterly impossible to make compatible the capability of printing in a large quantity or recording in colors finely, which requires a large size of the apparatus inevitably, and the capability of enhancing serviceability, which means downsizing and making the apparatus lighter.
Now, it is an object of the present invention to provide an ink supplying device (liquid supplying device) capable of adjusting negative pressure against the nozzle of a recording head to prevent ink from dropping down, among some others, without depending on the deformation of an ink tank in the system to supply ink from an ink tank to an ink jet head, and capable of contributing to downsizing the device as compared with the conventional structure, and also, to provide an ink jet recording apparatus (liquid discharge recording apparatus) that uses such ink supplying device.
In order to achieve the aforesaid object, the liquid supplying device of the present invention for supplying liquid to a recording head for discharging liquid comprises a liquid container (ink tank) for containing liquid (ink) to be supplied to the recording head; a first connecting portion for connecting the recording head and the liquid container; and a second connecting portion having one end thereof in the liquid container, and the other end thereof being open to the air outside. For this ink supplying device, the one end of the second connecting portion connected with the liquid container is positioned lower than the height of liquid discharge port of the recording head, and an interface between liquid and the air outside exists in the second connecting portion, and by the surface tension of meniscus formed on the interface, negative pressure is generated against the liquid discharge port of the recording head.
For this liquid supplying device, it is preferable to position the other end of the second connecting portion opened to the air outside higher than the one end thereof, and also, to position the other end of the second connecting portion opened to the air outside lower than the height of the liquid discharge port of the recording head. It is also conceivable that the first connecting portion and the second connecting portion extend from the bottom face of the liquid container downward, and are bent upward on the way, respectively.
Further, it is preferable to install a buffer chamber between both ends of the second connecting portion to provisionally retain liquid overflowing from the liquid container. In this case, it is desirable to arrange a liquid absorbent in the buffer chamber or to arrange the atmosphere-opening hole provided for the buffer chamber to be downward.
The liquid supplying device thus structured keeps the negative pressure constantly with the movement of the interface in the second connecting portion following the pressure changes inside the liquid container and recording head.
Further, the first connecting portion supplies liquid from the liquid container to the recording head when liquid in the recording head is consumed, and the second connecting portion induces the air outside into the liquid container when pressure in the liquid container is reduced.
As described above, the liquid supplying device of the present invention is provided with a liquid container (ink tank) that contains liquid (ink) to be supplied to a recording head; a first connecting portion that connects the recording head and the liquid container; and a second connecting portion having one end thereof in the liquid container and the other end thereof being open to the air outside, and one end of the second connecting portion connected with the liquid container is positioned lower than the height of the liquid discharge port of the recording head. Then, the structure is arranged so that there exists an interface between liquid and the air outside in the second connecting portion, and by the surface tension of meniscus formed on this interface, negative pressure is generated against the liquid discharge port of the recording head. In this way, liquid is prevented from being dropped down form the discharge port of the recording head. Further, it is arranged to move the interface in the second connecting portion in accordance with the changes in pressure in the liquid container and recording head so as to keep the negative pressure constantly. Therefore, it is unnecessary for the liquid container to deform. It can be a simple housing. The restriction of usable materials is small accordingly, and the manufacture is also simpler and executable at lower costs. Then, liquid can be filled in the liquid container up to its capacity, while it is unnecessary to secure space surrounding the liquid container, hence making efficiency extremely favorable in containing liquid. Also, there is no need for making the liquid supply device too large, thus contributing to saving space in the liquid discharge recording apparatus provided with this liquid supplying device.
Also, an liquid discharge recording apparatus, which is provided with the liquid supply device described above, and a recording head, and which performs recording by discharging liquid form the recording head to a recording medium, belongs to the present invention. With the structure thus arranged, it is unnecessary to make the liquid supplying device larger, thus implementing downsizing the liquid discharge apparatus as a whole. It is particularly effective for the liquid discharge recording apparatus that performs recording in a large quantity or fine color recording.
Also, with the provision of a buffer chamber that retains liquid provisionally between both ends of the second connecting portion, the buffer chamber functions to be receptacle for liquid that may be pushed out of the liquid container due to the expansion of air in the liquid container when temperature rises, thus preventing the inside of the recording apparatus from being stained by liquid contained in the liquid container.